1. Introduction

Organic chemistry is the branch of chemistry that studies carbon-containing compounds, except for a few simple carbon-containing substances such as CO, CO₂, carbonates, bicarbonates and carbides. Historically, it was believed that organic compounds could only be produced by living organisms — a belief called the Vital Force Theory. In 1828, Friedrich Wöhler synthesized urea (an organic compound) from ammonium cyanate (an inorganic salt), disproving the Vital Force Theory and showing organic compounds can be made from inorganic materials.

2. Sources of Organic Compounds

1. Natural (biological) sources: plants (sugars, starch, oils), animals (proteins, fats).
2. Fossil fuels: coal, petroleum (crude oil), natural gas — major industrial sources of hydrocarbons and related organic chemicals.

3. Special Properties of Carbon

• Catenation: carbon’s ability to form strong C–C bonds and make long chains and rings.
• Bond strength and variety: carbon forms stable single, double and triple bonds (C–C, C=C, C≡C) and bonds with many other elements (H, O, N, etc.).

4. Classification of Organic Compounds

Broadly, organic compounds are classified into:

5. Structural Representation of Organic Molecules

• Molecular formula: shows types and numbers of atoms (e.g., C₂H₆O).
• Condensed formula: compact structural form (e.g., CH₃CH₂OH for ethanol).
• Structural formula: shows each atom and bond explicitly (useful to see connectivity).

6. Alkyl Radicals

An alkyl radical (or alkyl group) is formed when a hydrogen atom is removed from an alkane, leaving an open bond. Example: methyl group CH₃– (derived from methane CH₄ by removing H).

7. Homologous Series

A homologous series is a family of compounds with the same functional group and similar chemical properties; successive members differ by a –CH₂– unit. Example (alkanes):

1. Methane — CH₄
2. Ethane — C₂H₆
3. Propane — C₃H₈
4. Butane — C₄H₁₀

8. Isomerism

Isomers are compounds with the same molecular formula but different structural arrangements. Types include structural (constitutional) isomers and stereoisomers (not covered in depth here). Example: C₄H₁₀ has two structural isomers:

• n‑Butane (straight chain)
• Isobutane (2‑methylpropane) (branched chain)

9. Important Examples & Simple Formulas

10. Short Questions & Model Answers

1. What was the Vital Force Theory?

   It was the idea that organic compounds could only be produced by living organisms using a special “vital force”.

2. How did Wöhler disprove the Vital Force Theory?

   Wöhler synthesized urea (an organic compound) from ammonium cyanate (an inorganic salt) in the laboratory (1828), showing organic compounds can be prepared from inorganic materials.

3. Define catenation.

   Catenation is the ability of carbon atoms to bond to each other, forming long chains and rings.

4. Give an example of structural isomerism.

   C₄H₁₀ → n‑butane and iso‑butane (2‑methylpropane).

5. What is a functional group? Give examples.

   A functional group is an atom or group of atoms that gives a compound its characteristic chemical properties. Examples: –OH (alcohol), –COOH (carboxylic acid), –NH₂ (amine).

6. Example of an alkyne?

   Ethyne (C₂H₂).

11. Suggested Study Tips

• Memorize general formulas and simple series (alkanes, alkenes, alkynes).
• Practice drawing structural formulas and identify functional groups.
• Use the condensed formulas to convert between molecular and structural forms.
• Solve textbook exercises and past paper questions for practice.